复合干摩擦的准零刚度隔振系统的亚谐共振

利用增量平均法研究了复合干摩擦阻尼器的准零刚度非线性隔振系统在外部简谐激励作用下的1/3次亚谐共振. 首先利用平均法得到了复合干摩擦的准零刚度隔振系统的主共振近似解析解, 然后在系统主共振近似解析解的基础上将系统的亚谐共振响应看作增量, 并利用平均法得到了准零刚度隔振系统的亚谐共振近似解析解. 利用李雅普诺夫方法得到了准零刚度隔振系统主共振和亚谐共振稳态解的稳定性条件, 并推导了系统1/3次亚谐共振的存在条件. 根据近似解析解分别得到了复合干摩擦的准零刚度隔振系统的主共振和亚谐共振力传递率. 利用数值解验证了准零刚度隔振系统主共振和亚谐共振近似解析解的准确性. 利用系统的近似解析解详细分析了准零刚度参数和干摩擦力对系统主共振和亚谐共振的幅频响应以及力传递特性的影响. 分析结果表明, 通过选取合适的干摩擦力参数, 可以消除准零刚度隔振系统在主共振区域的亚谐共振. 通过复合干摩擦阻尼器不但可以提高准零刚度隔振系统在低频区域的振幅抑制效果, 而且可以降低准零刚度隔振系统的起始隔振频率, 但是会增大系统在有效隔振频带内的力传递率.      

柔性基础准零刚度隔振系统动力学特性分析

为解决工程实践中的低频振动问题,提出了利用柔性基础准零刚度隔振系统对其进行隔离的方法。根据舰船装备实际情况,建立了柔性基础准零刚度隔振系统的动力学模型,利用谐波平衡法和平均法对动力学方程进行了求解,得到了谐波力激励下系统的幅频特性曲线和力传递率。研究了不同激励力幅值、质量比和阻尼比对系统隔振性能的影响。仿真结果表明,相比相应的等效线性隔振系统,通过适当地减小激励幅值和适当地增大质量比、阻尼比,柔性基础准零刚度隔振系统具有更优越的低频隔振性能,隔振起始频率较低,振动衰减率较大。     

一种基于SMR主动隔振模型的功率流控制方法

用功率流指标描述主动隔振系统中能量的传输，以传输到接受性的功率流最小为最优化控制目标，推导主动隔振系统中功率流传递的最优控制表达式，提出一种基于SMR主动隔震模型的主动功率流的最优化控制策略，对比分析了被动和主动模型下总功率流的传递特性以及主动控制时传递到基础的各功率流分量的分布特征。针对工程实际中的柔性安装问题，对四边筒支矩形薄板扩动隔振进行了研究。     

气动八作动器隔振平台的主动隔振研究

多自由度隔振平台可以有效地隔离运载器传递到卫星的振动载荷。本文采用气动八作动器隔振平台实现卫星的六自由度隔振。首先应用牛顿欧拉法建立了气动八作动器隔振平台的动力学模型,设计了平台的主动控制律,然后对平台的主、被动隔振特性进行了仿真分析。仿真分析和实验结果显示主动隔振使平台各方向的低频隔振性能均得到改善。     

被动隔振体非线性振动的能量迭代解法

研究了由基础振动激励、弹性材料隔离的被动隔振体的强非线性动力响应。用变形的三次多项式函数表征隔振材料的非线性刚度特性,建立了被动隔振体的非线性动力学方程,得到有阻尼受迫振动Duffing方程。将求解强非线性自治系统的能量迭代方法加以改进,推广应用到强非线性非自治系统,求出周期响应的近似解析解表达式,以及幅频关系、相频关系和隔振系数的近似表达式。算例中应用本方法与Runge-Kutta方法进行了对照,结果表明求解精度较高。本文利用计算机进行了辅助推导。     

机器—基础柔性隔振系统的功率流试验研究

在对楼层安装机器柔性耦合动力系统功率流理论研究的基础上，本文进一步从实验观点研究了机器—基础柔性隔振系统的功率流传递谱。建立了柔性隔振系统实验模型和功率流测试分析系统，从能量观点对机器—隔振器—弹性基础耦合系统的振动传递机理进行了实验研究。通过对称和非对称系统的功率流对比实验，揭示了功率流传递谱的非对称效应，验证了理论分析的正确性。     

磁致伸缩主被动隔振装置中的磁机耦合效应研究

磁致伸缩材料和柔顺位移放大机构组成的主动驱动装置具有精度高、驱动力大等特点.将其与被动隔振装置并联,形成主被动隔振装置,可以弥补纯被动隔振在低频和微幅扰动工况下的不足.本文针对这类磁致伸缩主被动隔振装置进行磁机耦合效应研究.基于Jiles-Atherton模型,分析了磁致伸缩材料所受应力对有效磁场、磁化强度、磁致伸缩系数和材料杨氏模量的影响,表征了材料磁机耦合效应.在此基础上,建立了主被动隔振装置的动力学模型,分析了主动驱动装置与被动隔振装置间的耦合作用.在耦合作用影响下,若被动隔振装置刚度不同,即使输入磁场相同,驱动器产生的驱动位移和驱动力也不相同.磁致伸缩材料的变刚度效应使隔振装置整体等效刚度不再为定值,从而影响被动隔振效果.本文提出了通过柔顺机构参数设计减小前述两种耦合影响的方法.数值仿真结果表明,磁致伸缩主被动隔振装置在低于、接近和高于谐振频率三类扰动下,都能达到比被动隔振更好的振动抑制效果.此外,仿真结果验证了考虑磁机耦合效应的数值模型具有更高精度.     

磁致伸缩主被动隔振装置中的磁机耦合效应研究

磁致伸缩材料和柔顺位移放大机构组成的主动驱动装置具有精度高、驱动力大等特点.将其与被动隔振装置并联,形成主被动隔振装置,可以弥补纯被动隔振在低频和微幅扰动工况下的不足.本文针对这类磁致伸缩主被动隔振装置进行磁机耦合效应研究.基于Jiles-Atherton模型,分析了磁致伸缩材料所受应力对有效磁场、磁化强度、磁致伸缩系数和材料杨氏模量的影响,表征了材料磁机耦合效应.在此基础上,建立了主被动隔振装置的动力学模型,分析了主动驱动装置与被动隔振装置间的耦合作用.在耦合作用影响下,若被动隔振装置刚度不同,即使输入磁场相同,驱动器产生的驱动位移和驱动力也不相同.磁致伸缩材料的变刚度效应使隔振装置整体等效刚度不再为定值,从而影响被动隔振效果.本文提出了通过柔顺机构参数设计减小前述两种耦合影响的方法.数值仿真结果表明,磁致伸缩主被动隔振装置在低于、接近和高于谐振频率三类扰动下,都能达到比被动隔振更好的振动抑制效果.此外,仿真结果验证了考虑磁机耦合效应的数值模型具有更高精度.      

引力波探测中的被动隔振系统

介绍了引力波探测实验中的被动隔振系统的基本原理和研究现状,讨论其性能及特点.低频被动隔振系统,如七级气体弹簧隔振系统,多级隔振堆,四级悬臂弹簧隔振系统以及三级弯曲弹簧隔振系统在10Hz以上,都具有好的隔振性能;倒摆、折叠摆、 X摆和锥摆等超低频水平隔振系统实现了几十秒的共振周期;建立在对称扭杆弹簧系统基础上,构思新颖的被动垂直隔振系统克服了传统被动垂直隔振系统无法解决的困难,实现了超低频被动垂直隔振.      

一种直升机机载跟瞄系统被动隔振平台设计

隔振平台连接直升机机体与光电跟瞄吊舱,对机载跟瞄系统的跟瞄精度至关重要。采用多个笼形隔振器并联,设计了一种直升机机载跟瞄系统的被动隔振平台。由欧拉变换描述隔振平台的空间姿态,基于Lagrange方法建立隔振平台的动力学模型,获得了不同激振频率下隔振平台的振动传递率。利用ANSYS动力学仿真验证了隔振平台理论模型的正确性,校核了大过载情况下隔振平台的冗余保护能力。通过实际飞行测试,检验了隔振平台的隔振效果。     

基于波动法的框式结构功率流主动控制方法与实验研究

为了研究扰动影响下框式结构中的功率流传播与主动控制,首先采用波动方法建立了框式结构的动力学模型并获得了其在扰动下的精确动力学响应,进一步得到结构中传播的功率流,并以此为目标函数,优化得到了最优控制力的大小与相位,然后对结构施加最优控制力,实现了框式结构的功率流主动控制。对框式结构功率流主动控制方法进行了数值计算分析与实验验证。结果表明：采用波动方法计算框式结构的动力学响应精确可靠;通过数值计算与实验研究可知功率流主动控制可以明显降低框式结构全频域内的抖动,验证了基于波动方法功率流主动控制的正确性与有效性。     

浮筏隔振系统功率流特性分析

针对工程实际中浮筏隔振装置，建立了柔性基础上机组多支承弹性浮筏耦合隔振系统动力学普遍模型，提出了子系统动态特性综合分析法，给出了耦合系统动态传递方程及功率流表达式。根据工程中两机组浮筏隔振系统功率流理论计算结果，着重探讨安装频率与支承结构柔性耦合作用及其对隔振效果影响。研究结果表明：合理设计安装频率，可有效控制振动能量传输。     

复杂激励下平置板式浮筏功率流传递特性研究

针对隔振理论研究领域中舰船的振动和噪声控制问题，建立六维^[1、2]平置板式弹性浮筏的多机组隔振理论分析计算模型，导出了弹性浮筏传递功率流的表达式，从振动能量传输的角度来评价浮筏系统隔振效果，绘制了功率谱曲线，揭示机组的布置，筏架刚度等结构参数对功率流传递的影响，给出了浮筏设计中结构参数选择的一般准则。     

Structure- and fluid-borne acoustic power sources induced by turbulent flow in 90° piping elbows

The structure- and fluid-borne vibro-acoustic power spectra induced by turbulent fluid flow over the walls of a continuous 90° piping elbow are computed. Although the actual power input to the piping by the wall pressure fluctuations is distributed throughout the elbow, equivalent total power inputs to various structural wavetypes (bending, torsion, axial) and fluid (plane-waves) at the inlet and discharge of the elbow are computed. The powers at the elbow “ports” are suitable inputs to wave- and statistically-based models of larger piping systems that include the elbow. Calculations for several flow and structural parameters, including pipe wall thickness, flow speed, and flow Reynolds number are shown. The power spectra are scaled on flow and structural–acoustic parameters so that levels for conditions other than those considered in the paper may be estimated, subject to geometric similarity constraints (elbow radius/pipe diameter). The approach for computing the powers (called CHAMP – combined hydroacoustic modeling programs), which links computational fluid dynamics, finite element and boundary element modeling, and efficient random analysis techniques, is general, and may be applied to other piping system components excited by turbulent fluid flow, such as U-bends and T-sections.     

BBD板结构的振动功率流研究

多冲击体阻尼（下文简称ＢＢＤ）是结构振动、噪声控制中的一项新技术。本文基于它的作用机理和机械导纳与弹性结构动力学理论，推导了三种不同ＢＢＤ板结构振动功率流的解析表达式。并进行了数值计算，给出了测量验证结果。最后定量分析了ＢＢＤ对板结构功率流的影响。     

Effects of 3-D channel blockage and turbulent wake mixing on the limit of power extraction by tidal turbines

Three-dimensional incompressible Reynolds-averaged Navier–Stokes (RANS) computations are performed for water flow past an actuator disk model (representing a tidal turbine) placed in a rectangular channel of various blockages and aspect ratios. The study focuses on the effects of turbulent mixing behind the disk, as well as on the effects of channel blockage and aspect ratio on the prediction of the hydrodynamic limit of power extraction. To qualitatively account for the effect of turbulence generated by the turbine (rather than by the shear flow behind the turbine), we propose a new approach, called a blade-induced turbulence model, which does not use any additional model coefficients other than those used in the original RANS turbulence model. Results demonstrate that the power removed from the mean flow by the disk increases as the strength of turbulent mixing behind the disk increases, being consistent with the turbulent shear stress on the interface between the bypass and core flow passages acting in such a way as to decelerate the bypass flow and accelerate the core flow. The channel aspect ratio also affects the flow downstream of the disk but has less influence upstream of the disk; hence its effect on the limit of power extraction is relatively minor compared to that of the channel blockage, which is shown to be significant but satisfactorily estimated using one-dimensional inviscid theory previously reported in the literature.     

Performance modeling and analysis of blood flow in elastic arteries

Nomenclature　　τ　　wallshearstressγshearrateτy yieldstressηc Cassonviscosityktheconsistencyindexnnon_Newtonianindexτp shearstressofthepthelementωangularvelocityRvessel’sradiusCwavespeedM　　magneticparameter (Hartmannnumber)u,w　velocitycomponentinther_andz_directions,respectivelyP　　pressureα　　unsteadinessparameter k , R meanparametersTp relaxationtimeofthepthelementρ densityIntroductionTheimportancetoatherogenesisofarterialflowphenomenasuchasflowseparation ,recirculationands…     

On Aifantis’ strain gradient plasticity theory accounting for plastic spin

This paper examines the effect of codirectionality hypothesis on Aifantis’ distortion gradient plasticity theory. The system of microforces includes microstress, power-conjugate to the Burgers tensor rate. The proposed codirectionality hypothesis assumes, that the flow direction and the plastic microstress are in the same direction. It is obtained that the power expended by the microstress power-conjugate to the Burgers tensor rate, can be additively decomposed to power expended by scalar and vector microscopic stresses power-conjugate to the accumulated plastic distortion rate and gradient of plastic distortion rate respectively. Following the proposed codirectionality hypothesis, it is obtained that the microstress power-conjugate to the Burgers tensor rate is purely energetic. The obtained flow rule accounts for plastic spin and generalizes the Aifantis’ flow rule.     

Stall control at high angle of attack with plasma sheet actuators

We analyzed the modifications of the airflow around an NACA 0015 airfoil when the flow was perturbed with electrohydrodynamic forces. The actuation was produced with a plasma sheet device (PSD) consisting in two bare electrodes flush mounted on the surface of the wing profile operated to obtain a discharge contouring the body in the inter-electrode space. We analyze the influence of different parameters of the actuation (frequency, input power, electrodes position) on the aerodynamic performance of the airfoil, basing our study on measurements of the surface pressure distribution and of the flow fields with particle image velocimetry technique. The experiments indicated that at moderate Reynolds numbers (150,000 < Re < 333,000) and at high angles of attack, steady or periodic actuations enabled large improvement of the lift and drag/lift aerodynamic coefficients by reattaching the flow along the extrados. However, to attain the same results steady actuations required larger power consumption. When exciting the flow with a moderate value of non-dimensional power coefficient (ratio of electric power flow with the kinetic power flow), a frequency of excitation produced a peak on the coefficients that evaluate the airfoil performance. This peak in terms of a non-dimensional frequency was close to 0.4 and can be associated to an optimal frequency of excitation. However, our work indicates that this peak is not constant for all stalled flow conditions and should be analyzed considering scale factors that take into account the ratio of the length where the forcing acts and the cord length.